Re: [Qemu-devel] [qemu PATCH] hw/i386/pc_sysfw: support more than one flash drive

[Jordan Justen]

On Tue, Nov 26, 2013 at 5:32 AM, Laszlo Ersek <address@hidden> wrote:
> On 11/26/13 13:36, Markus Armbruster wrote:
>
>> Your stated purpose for multiple -pflash:
>>
>>     This accommodates the following use case: suppose that OVMF is split in
>>     two parts, a writeable host file for non-volatile variable storage, and a
>>     read-only part for bootstrap and decompressible executable code.
>>
>> Such a split between writable part and read-only part makes sense to me.
>> How is it done in physical hardware?  Single device with configurable
>> write-protect, or two separate devices?
>
> (Jordan could help more.)
>
> Likely one device that's fully writeable.

Most parts will have a dedicated read-only line.

Many devices have 'block-locking' that will make some subset of blocks
read-only until a reset.

In addition to this, many chipsets will allow flash writes to be
protected by triggering SMM when a flash write occurs.

Using multiple chips are less common due to cost, but this is not a
factor for QEMU. :)

-Jordan